Why Does My Car Alarm Keep Going Off?
- Diagnostic
FixMyCar troubleshoots why your car alarm might be going off, what you should do in this scenario, and who to contact to fix the problem.
Book a car repair nowCharlotte Phillips
Tuesday September 24 2024
7 min read
Having your car alarm go off for seemingly no reason is a stressful experience, especially if it happens at night. The last thing you want to do is wake up your neighbours. You need to find a solution fast - but why is it happening, and what can you do? Read on to find out.
Contents
How do I know if my car has an alarm?
Can my car alarm go off by itself?
Why does my car alarm keep going off?
How to stop your car alarm going off
In a nutshell: Your car alarm could be going off due to a low car or key fob battery, faulty wiring or sensors, doors that aren't closed properly or poor installation. Read on to find out how to stop your alarm going off.
Why are car alarms important?
Car alarms can be annoying when they go off for no reason, but the loud noise and flashing lights are crucial for keeping your car safe. They deter thieves by attracting attention from passers-by if someone tries to break in.
Most cars come fitted with an alarm system as standard. There are other methods you can use to keep your vehicle safe, too, such as:
Parking in a garage or well-lit area.
Locking all doors and windows.
Using an anti-theft immobiliser.
Fitting a steering wheel lock.
How do I know if my car has an alarm?
When working correctly, your car alarm should only go off if someone tries to break in, so there's a good chance you've never heard it before. In that case, you may wonder whether your vehicle has an alarm and whether it's working correctly.
There are a few ways you can check:
Look in your car manual - it should include information about any alarm systems fitted by the manufacturer.
Check your key fob - there might be a button you can press to activate the alarm.
Ask at your next service - the next time you take your car for an MOT or service, you could ask the mechanic to check or phone your local dealership to find out.
Look for a dashboard light - some cars have a small light that flashes to indicate the alarm system is armed and ready.
Can my car alarm go off by itself?
Your car alarm can go off for several reasons, ranging from a low key fob battery to a faulty lock sensor. We'll cover each possibility in more detail below.
Why does my car alarm keep going off?
1. Low car battery
When your car's battery is low on power, it won't send the correct voltage to the alarm system, which could trigger the alarm. A similar thing can happen when the battery is corroded or dirty, interfering with the flow of electricity.
One effective solution to a low car battery is jump-starting your car and allowing it to charge by driving it for half an hour. This method can often resolve the issue, saving you the cost of a battery replacement, although it isn't always effective.
Read about what to do when your battery is dead.
How much does it cost to fix?
The average price of a battery replacement is £225.93, according to our data.
2. Faulty wiring
One of the most common reasons for a car alarm that keeps going off is a problem with the wiring. If this is the issue, you'll need to contact an auto electrician for a repair.
How much does it cost to fix?
According to our data, the average price of an electrical fault repair is £79.11.
3. Flat key fob battery
The batteries in your key fob won't last forever. Eventually, they'll go flat, which could prevent the key from sending signals correctly, making the alarm go off. Replacing the batteries is easy - you can buy new ones from almost any shop that sells batteries, and the key fob can be opened using a screwdriver.
Information about the type of batteries needed can be found in your owner's manual.
How much does it cost to fix?
New batteries should cost less than £10.
4. Faulty sensors
Modern cars are fitted with hundreds of sensors, several of which are used by the alarm system. These include:
Door lock sensors
Tilt sensors
Proximity sensors
Shock sensors
Glass break sensors
Microphone sensors
If just one of these sensors fails or is overly sensitive, it could trigger the car alarm. You'll need the help of a mechanic to work out which sensor is to blame.
How much does it cost to fix?
On average, a sensor repair costs £95.09 when you book through FixMyCar.
5. Doors not closed properly
Similarly, not having your car doors closed properly could trick your car into thinking that the door lock sensor has been triggered, making the alarm system go off. If one of the doors isn't secured, you'll see a warning light on the dashboard.
6. Poor installation
If your car is old, it might not have been fitted with a factory alarm. Instead, it could be equipped with an aftermarket alarm that hasn't been installed correctly. It's easy to make mistakes when fitting an alarm system yourself - and if the job isn't done right, it could invalidate your insurance, so it's worth having the problem checked out by a mechanic.
How much does it cost to fix?
It's best to contact an auto electrician to inspect the alarm system. On average, drivers who book a car alarm repair through FixMyCar pay £79.45.
How to stop your car alarm going off
You can try some of the following steps to stop your car alarm from going off:
Lock and unlock the driver’s side door with the key. You may be able to shut off the alarm by unlocking the door with the correct car key. If remotely unlocking it doesn't work, try using the physical key - it's usually tucked away in the fob.
Start the car. Using the key to start the car can reset the alarm, providing a temporary fix while you figure out a more permanent solution.
Read your owner’s manual. Some cars have a more complicated process for shutting off the alarm system. If you're unsure, the best thing to do is to read your owner’s manual. There could be an 'off' button on the dashboard that you can use to switch the alarm off manually.
Switch off the battery. The final option is to starve the alarm of power by disconnecting the car's battery. Simply remove the negative battery connector from the battery.
Disconnecting the battery should be a last resort because it could mess up the onboard computer and infotainment system.
What are the risks of turning off your car alarm?
Switching off your car alarm is a risky thing to do, so you should weigh up the pros and cons first. Consider the following:
The physical act of disconnecting the alarm could cause harm to your vehicle.
Your car will be much easier to steal.
Your insurance could be impacted if you don't have an alarm.
There are less likely to be witnesses in the event of theft because the alarm won't have notified people nearby about what's happening.
What to do if your car alarm keeps going off
It goes without saying that car alarm noise is annoying for you and your neighbours. But did you know that the council can also consider it a statutory nuisance?
Your local council could issue you a notice and forcibly remove the vehicle, charging you for any costs.
Additionally, if your alarm keeps going off and is faulty, it could invalidate your insurance if you try to claim. For these reasons, we recommend getting your alarm system checked by a trained professional.
If you have any other issues with your car that you'd like to try and diagnose yourself, check out our guide on self diagnosing car problems. The more you know about how your car works, the better.
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